The findControl method is not able to find controls when called inside of the event handler for the OnGridCreated event as follows. This will cause an error because findControl() returns null. Shouldn't the controls be loaded at this point? Note that I am able to find controls in the row selected/deselected event handlers.
function gridCreated(sender, args)
{
for (var i = 0; i <= sender.get_selectedItems().length - 1; i++)
{
sender.get_selectedItems()[i].findControl("rntbMinDistance").enable();
}
}